Technical Abstract:
Understanding rainfall characteristics and a watershed's response to that rainfall is essential in hydrological modeling, and especially to meet the goals of the USDA's Conservation Effects Assessment Project (CEAP). Excess rainfall was estimated using the O- index and 15-min rainfall and direct runoff (separated from streamflow) data from the Little Washita River Experimental Watershed (LWREW), located in south central Oklahoma. Data were extracted through a prototype of the CEAP data system, STEWARDS, to facilitate manipulation of a large volume of data. A transfer function was used to model rainfall-runoff response. The transfer function shape (width and height) characteristics and runoff coefficients (runoff to total rainfall ratio) in three sub-watersheds of different sizes were examined for the 2005-2006 study period. The study results indicate that the characteristics of the transfer function and runoff coefficients depend upon rainfall excess and runoff may be useful for SWAT model calibration by comparison to model simulations.